Electric crucible-furnace.



D..F. CALHANB. i ELBGTRIG GRUGIBLE FURNAGE.

APPLIUATIOF FILED NOV. 3, 19.711.

Patented Mar. 31, 191.4.

2 SHEETS-BHEET 1.

LA K l0" Z2 ll D. P. GALANE. ELECTRIC CRUGIBLE FUENACE. APPLIOATION FILED Nov. a, 1911.

Patented Mar.31,1914.

2 SHEETS-SHEET 2.

ffe 27,2355

1 'iwmmiliesieaatmaf-,--1

To-lzwlhomt may/concern: l -4 s y Be it known that I, DAN F, CALHA'NE, acitizen 'of the United States residing at Worcester in the county of orcester and State of r assachusetts, have invented a new and useful4 .Electric Crucible-Furnace, of which the following is a lspecification.

This invention relates to an electric furnace suitable for very hi h temperatures."-

The principal objects o the invention are to provide a convenient and'inexpensive construction for this purpose in which the heat shall be concentrated along the walls of the crucible by forcing the current to flow in a restricted path therealong so as to increase the eciency and the practicable limit of the working temperature; to providemeans whereby this concentration can be caused to take place at any desired plane along `the wall of the crucible'and throughout any` desired zone thereof; to rovide a construction in which'the current s all be caused to flow alon the crucible walls without unduly heating the bottom; to provide for adjusting the support of the crucible and said concentrating means so that crucibles` of different sizes can be used without altering thefurnace; to employ an improved refractory4 material, as the crucible support and means for concentratin the heat as set forth above; to provi e improvements` in eliiciency of heat insulation; and to provide an improved form of concentric sets of crucibles nested to ether so that the furnace can be continuous o erated for melting the charges of a p ura ity of crucibles without disturbing the carbon core of the furnace and without allowing it to cool down.

Further objects and advantages of the invention will appear hereinafter.

Reference is to be had to the accompanying drawings in which- Figure 1 is a vertical central sectional view of a preferred formof crucible furnace constructed in accordance with this invention, and Fig. 2 is a similar view of a modied form.

In the form shown' in Fig. 1 the furnace is constructed with an exterior cement wall 10 inside which is an asbestos filling 11 separated into an outer and inner member by a la er of asbestos boards 12. 0n the inside of t ese is a clay wall 13. These parts ref' erably are4 substantially cylindrical in orm butA that of course not material. rlfhe eicien'cy in heat insulation ofthe successive i collection Letters intent; l,Maximum'alea imainm alan;unaufaesaaoc.'

'. f onUcinLn-rnnnncnfj atenten Mar. 315.1914.

` walls 4o fasbestoa packing insidefthe concrete walls 1s one.. advantage vof this invention.-

The space 4inside the clay' wall isfprovi'ded with -a cement` block 14 to form the bottom thereof. Above Vthis block isa carbon core 15 preferably formed of powdered carbon and constituting `a Backing for the crucible or t e current. At the bottrode 16. rThis is connected with a source of current through a circular terminal 17 or the tlike, shown as having a central hub and radial spokes. Inside/the annular electrode is a block 18 of insulating material; (alundum). This block is shown as comprising a plurality y of inde endently removable parts of different heig ts superimposed one on y'the other so that anyl desired part can be used to support the bottom of the crucible 19 and bring its bottom to different heights v above the bottom of the furnace. By this means the furnace can be used to accommodate crucibles of different sizes. The separate blocks of which this support is made up preferably have mortises and tenons formed at their ends so that they can easily be piled up vertically. At the top of the carbon packing another circular graphite electrode 20 is located similar to the electrode 17 .l This is preferably annular in form also. The electrodes are of graphite chiefiy because it is more easily machined thanother forms of carbon. This furnace is provided with a cla cover 21 as usual.

Located in the car n core or packing are a series of insulating rings 23 each of annular f rm and arranged to substantially fill the s ace between the crucible and the clay wall 13. By means ofI these rings the current is forced to be concentrated in a small space along `the walls of the crucible and consequently tends to heat this s ace higher than it would if diffused throug out the space between the clay walls`13. At the same time it causes all this heat to be utilized for the purpose of raising the temperature of the crucible and melting its contents)` In this way the eiciency of the device is very greatly increased. In addition in a floating condition; that is at any point within-the carbon core 15, it is obvious to this by vhaving these rings substantially.v

that the plane of concentration of the heat can be located either high or low on the crucible. If the crucible contains only a small charge to be melted5 obviously this touring. In-'a' ditionl to this feature, 1t Ywill be creased jr decreased undesired. In this way observed that'this-in'ulati vlione is'made up of af plurality of thin rings be remov and replaced at w1 r extent of the concentrated zone can a maximum eicienc is secured. It will be observed thatthe a. justability of the sup: portfonthe crucible coperates with t e adjuetabil-ityV of the insulatmgrings 23 to permit cruclbles of different slzes to be used in aslng'le furnace.y I have found 1n practice that'for )'tle high\'tem creatures for which this 'furnace is designe alundum is the best material for these rings as 1t lsal'so for the blocks or supporttlS.` fAlundum of course, as is understood, is an artificial' ccrundum, oxid of aluminum. By the use of alundumV for these purposes both a support for the crucible and a deliector for the heat are secured whichlare of suitable construction, not liable to become friable at the surface after repeated heatings to its` melting point, and at the same time they are of a material having a melting point well above that required for ordinary operatlons in` a furnace of this' kind. I find in practice moreover,"`that the -crucible canbe heated to i the temperature of melting of alundum without greatly dama ingthe alundum 1nsulating rings 23 or t e blocks 18." Thls 1s due to the fact that the intense heat zone is mainly between the Walls of the crucible and the rings. i The alundum rings preferably are spaced in the vicinity of a quarter of an inch from the crucible. The crucible preferably is pressed 'alunduln containing a minimum of ay. This furnishes insulation within the heated zone and prevents the loss of eiciency bythe diversion of the current threugh 'the lcrucible walls.

i Ano her `f eatur`e of theinvention consists I in the 'provision of a nest of crucibles. In

this'casefthecrucible 19' is shown as of ordinary foif'ni'but'within it is located a second -c1r`1`1cible'25, having a shoulder 26 resting; on the top of the lcrucible 19' and 1ts interior with an de- Qs'ired degree o Anicet When the charge in the crucible 25A- has een melted the cover 21 can be reinelved'and this crucible taken out, lea-ving the crucible 19 already heated to a high temperature and ready to receive which .cani 1 se therebewith 'a lining 27 of magnesia.

Inthe' form shwn in-Fig. 2 the arrange- 'tallsof the'` vfurnace are made of a plurality @of fire bricks 3Q. 'Inside` this is a body 31 of "Portland"cementJ magnesia oxidhnd asbesl tos,forming `the sides and bottom,l Inside 'this is a--re cla-y mulile32, iron' bound. The alundum ,blocks -18 are used as in Fig. 1.-

llhe two" eletrodesare gra hte-rings 33 `The crucible 25 is shown as'beingprovided l.

Lmentis somewhatsimpler as the external.

and 34.. Ihe core 35,.is ma e as in Fig. 1,

and a concentratinginsulatin ring 23 is shown formed of al'undum.` 'Q viously'this ring is separated from the' crucible by conducting 'material topermit the current to flow between them and to be concentrated along the -wall 'of the crucible adjacent to the ring. In this case a graphite crucible 36 is shown as having analundmn lining 3'( to keep the melts from carbon contamination.

In act-ual use itis believed that this -furnace has been raised to a temperature of about 2800 degrees centigrade. It has at least been up to a 'point high enough to fuse alundum. v

Although I have illustrated and described two preferred forms of the invention, I am aware that other modifications can be made therein 'without' departing from the scope of the invention as expressed in the claims. Therefore, I do not wish to be limitedto all the details of construction shown and described, but

i What I do claim is 1 As an article of manufacture, av cruci-` ble furnace having an exterior cement Wall, a wall inside the same of asbestos filling having a partition of asbestos board intermediate between its outer and inner surfaces, an inner wall 4of solid insulating material, a cement bottom inside the inner IWall, an electrode on the cement bottom, andan'electrode at the top of the furnace. f

2. As an article of manufacture, a crucible fur'ace having insulating On5aining Walls, an electrode .at the bottom ofthefurnace and one at'thetop, a plurality of removable and replaceable solid vinsulating blocks superimposed one upon the other' at the bottoml of the furnace for supporting a crucible, a continuous granular ayc'king around the blocks and crucible, an a' plurality of independently removable insulating rings located one above the other surrounding the crucible, whereby the height of the crucible can be adjusted by 'removing and replacing the blocks and the zone of the crucible effected by the insulating rings' can b e regulated by remoying'and replacing the rings.

'3. As an article of manufacture, a cruci'f bl furnace having insulating 'containing yvalls, means for s upprtin'g' a'crncibletheifef mill?. dlfQlQIl-.t'lleflgh llf@ @Said zllli',

iso

a resistor for receiving the Crucible and conductin the current and a lurality of ndepen ently removable insu ating rings 1ocated in said resistor and extending 'substantially to the walls of the ,Crucible for concentrating the current and heat along any desired portion thereof vertically.

4. As an article of manufacture, a crucible furnace having 4insulating containing walls, means for supporting a Crucible, a resistor for receiving the Crucible and conductin the current, and aplurality of indepen ently removable insulating rings located in said resistorv and extending substantially to thev walls of the Crucible for concentrating the current and heat along any desired zone thereof.

5. In a Crucible furnace, the combination of insulating containing walls, an electrode at the bottom, removable and replaceable blocks of alundum superimposed at the bottom, a Crucible on said blocks, a continuous carbon packin around the blocks and crucible, a plura ity of separately removable alundum rings located within said packing for directing the current and concentrating the heat along the walls, and a second electrode in Contact with the carbon packing.

6. As an article of manufacture, an electric furnace comprising electrodes, and a refractory Conductor between tliem having a ring of alundum located therein.

In testimony whereof I have hereunto set my hand, in the presence of two subscribing witnesses.

DANIEL F. CALHANE.

WVitnesses:

ALBERT E. FAY, C. FoRREs'r WnssoN. 

